System and method for controlling radio frequency transmissions from an electronic device

ABSTRACT

The invention relates to a system and method for attenuating harmonics in output signals. In the system, an electronic circuit for reducing harmonics of an output signal from a power amplifier in a transmission circuit for a wireless communication device is provided. The circuit comprises: a printed circuit board (PCB); a power amplifier for generating an output signal; and a circuit implemented on the PCB connected to an output terminal of the power amplifier for the output signal. The circuit comprises a first filtering stage; a delay element; and a harmonic filter. The delay element is located between the harmonic filter and the output terminal and the delay element provides a timing delay in the output signal through at least one 0 ohm-rated component. Also, the harmonic filter is a low pass filter having a frequency cut-off point that attenuates first order harmonics of the output signal.

The invention described herein relates to a system and method forcontrolling and adjusting output of a transmission of a transmittedradio frequency (RF) signal originating from a power amplifier in anelectronic device to reduce levels of harmonics.

BACKGROUND

Current wireless handheld mobile communication devices perform a varietyof functions to enable mobile users to stay current with information andcommunications, such as e-mail, corporate data and organizer informationwhile they are away from their desks. Frequently such devicescommunicate with other devices using wireless transmissions. Suchtransmissions are generated by internal amplifiers and are transmittedthrough one or more antennae on the device. It is a common requirementthat certain jurisdictions regulate transmission aspects of wirelessdevices. For devices sold in the United States, the FederalCommunications Commission (FCC) regulates electrical characteristics ofsuch transmissions. A set of FCC regulations imposes limitation on theamplitude of harmonics generated by such transmissions. Existingtransmission circuits in communication devices tend to generate largesignal harmonics around the fundamental transmission frequency. Theseharmonics may generate additional radio frequency noise that may not bein compliance with FCC regulations. There are usually three main sourcesof radio frequency noise from a power amplifier: signal harmonicspresent in the output signal of the power amplifier; harmonics and ornoise generated due to a power and/or impedance mis-match between theoutput of the power amplifier and its related output circuit; and radiofrequency transmissions generated from signals leaking from the inputpower circuit through the circuit traces on the printed circuit board(PCB) connecting the power amplifier to a power source (e.g. a battery,such as a lithium ion battery) and radiating from the device through thebattery (e.g. through the case of the battery).

There is a need for a system and method which addresses deficiencies inthe prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of an electronic device having aradio frequency (RF) transmission module in accordance with anembodiment;

FIG. 2 is a block diagram of certain internal components and the RFtransmission module of FIG. 1;

FIG. 3 is a block diagram of the RF transmission module of the device ofFIG. 1;

FIG. 4 is a schematic diagram of the RF transmission module of FIG. 3;

FIG. 5A is a Smith chart of original impedance presented to an output ofa power amplifier of a prior art system;

FIG. 5B is a Smith chart of the impedance presented to the output of thepower amplifier with delay element added to the transmission module ofFIG. 3; and

FIG. 6 is a schematic diagram of additional circuits relating to the RFtransmission module of FIG. 2.

DETAILED DESCRIPTION OF AN EMBODIMENT

The description which follows and the embodiments described therein areprovided by way of illustration of an example or examples of particularembodiments of the principles of the present disclosure. These examplesare provided for the purposes of explanation and not limitation of thoseprinciples and of the invention. In the description which follows, likeparts are marked throughout the specification and the drawings with thesame respective reference numerals.

In a first aspect, an electronic circuit for reducing harmonics of anoutput signal from a power amplifier in a radio frequency transmissioncircuit for a wireless communication device is provided. The circuitcomprises: a printed circuit board (PCB); a power amplifier forgenerating an output signal for the communication device; and a circuitimplemented on the PCB connected to an output terminal of the poweramplifier for the output signal. The circuit comprises a first filteringstage; a delay element and a harmonic filter. In the circuit, the delayelement is located between the harmonic filter and the output terminaland the delay element provides a timing delay in the output signalthrough at least one 0 ohm-rated component. Also, the harmonic filter isa low pass filter having a frequency cut-off point that attenuates firstorder harmonics of the output signal.

In the electronic circuit, the delay element may be a 0 ohm component.

In the electronic circuit, the delay element may replace a component ofa filter element in the circuit.

In the electronic circuit, the harmonic filter may implement the filterelement that the delay element replaced.

In the electronic circuit, the filtering stage may comprise a notchfilter to attenuate signals about a specific frequency band, such as the5 GHz frequency band.

In the electronic circuit, the filtering stage may further comprise alow pass filter to attenuate signals over a specific frequency band,such as the 5 GHz frequency band.

In the electronic circuit, the delay element may replace a filterelement in the circuit by utilizing an inductor in place of a componentof the filter element.

In the electronic circuit, the delay element may comprise an alternativetrack in the PCB that is selectively connected to the circuit byinsertion of at least one 0 ohm component to complete an electronicconnection between the track and the circuit.

The electronic circuit may further comprise capacitors to reducetransmission of signals from the power amplifier in tracks in the PCB ofa power connection circuit connecting the power amplifier to a batteryfor the amplifier.

In the electronic circuit, a set of the capacitors may be located in thepower connection circuit between a high filter choke and the poweramplifier. Further, the capacitors may provide a low pass filter toattenuate signals over the 2 GHz frequency band.

Additionally or alternatively, in the electronic circuit, capacitors maybe located in the power connection circuit between the high filter chokeand battery. Further, the capacitors may provide a low pass filter toattenuate signals over the 2 GHz frequency band.

Additionally or alternatively, the delay element may be a track in thePCB that has sufficient length providing a propagation delay for asignal to traverse the length to provide the timing delay.

Also, in the circuit, an input point of the circuit may be tuned toaccommodate power and impedance characteristics of an output of thepower amplifier.

In a second aspect, a method of reducing harmonics of an output signalfrom a power amplifier in a radio frequency transmission circuit for awireless communication device is provided. The method comprises:providing a first filtering stage for the output signal; providing aharmonic filter to the output signal after the first filtering stage;providing an output stage for the output signal after the harmonicfilter; and providing a dedicated delay element before the harmonicfilter for the output signal to impart a time delay for the outputsignal, causing harmonics of the output signal to be reduced. In thecircuit, the harmonic filter is a low pass filter having a frequencycut-off point that attenuates first order harmonics of the outputsignal.

In the method, the delay element may be a 0 ohm component.

In the method, the delay element may replace a component of a filterelement in the circuit.

The method may further comprise filtering transmission of signals fromthe power amplifier in a power connection circuit connecting the poweramplifier to a battery for the amplifier.

The method may further implement features of circuits described in otheraspects.

In other aspects, various combinations of sets and subsets of the aboveaspects are provided.

Generally, an embodiment provides a system and method for controllingthe output of an RF transmission module of a wireless device. Inparticular, the RF transmissions are controlled such that harmonics ofthe output signal around their fundamental frequencies are dampened. Anembodiment utilizes a delay element in the output circuit of an RFtransmission to introduce a timing delay to the output signal for the RFtransmission before it is provided to the antenna of the device. As willbe seen, the delay introduces a time delay to the output signal, whilemaintaining the amplitude of the output signal, which has the effect ofdampening harmonics relating to the fundamental frequencies of theoutput signals.

Exemplary details of embodiments are provided herein. First, adescription is provided on general components of a device thatincorporates an embodiment. Next, further detail is provided onexemplary features of a circuit for an embodiment.

FIG. 1 provides general features of a portable, electronic device inaccordance with an embodiment, which is indicated generally at 10.Device 10 is based on a computing platform having functionality of anenhanced personal digital assistant with a cellphone and can receive andtransmit wireless communications, including as email, SMS and voicecommunications. Electronic device 10 can be based on construction designand functionality of other electronic devices, such as smart telephones,desktop computers, pagers or laptops having telephony equipment. In apresent embodiment, electronic device 10 includes a housing 12, an LCD14, speaker 16, an LED indicator 18, a trackball 20, an ESC (“escape”)key 22, keypad 24, a telephone headset comprised of an ear bud 26 and amicrophone 28. Trackball 20 and ESC key 22 can be inwardly depressedalong the path of arrow “A” as a means to provide additional input todevice 10. It will be understood that housing 12 can be made from anysuitable material as will occur to those of skill in the art and may besuitably formed to house and hold all components of device 10.

Further detail is provided on components of device 10. Device 10 isoperable to conduct wireless telephone calls, using any known wirelessphone system such as a Global System for Mobile Communications (GSM)system, Code Division Multiple Access (CDMA) system, CDMA 2000 system,Cellular Digital Packet Data (CDPD) system and Time Division MultipleAccess (TDMA) system. Other wireless phone systems can include Bluetoothand the many forms of 802.11 wireless broadband, like 802.11a, 802.11b,802.11g, etc. that support voice. Device 10 is a quad-band compatibledevice providing wireless communication capabilities with networksoperating in any one or more of the 800, 900, 1800 and 1900 MHzfrequency broadcast bands. Other embodiments include Voice over IP(VoIP) type streaming data communications that can simulatecircuit-switched phone calls. Ear bud 26 can be used to listen to phonecalls and other sound messages and microphone 28 can be used to speakinto and input sound messages to device 10.

Referring to FIG. 2, functional components of device 10 are provided inschematic 200. The functional components are generally electronic,structural or electro-mechanical devices. In particular, microprocessor202 is provided to control and receive almost all data, transmissions,inputs and outputs related to device 10. Microprocessor 202 is shownschematically as coupled to keypad 24 and other internal devices.Microprocessor 202 preferably controls the overall operation of thedevice 10 and its components. Exemplary microprocessors formicroprocessor 202 include Data 950 (trade-mark) series microprocessorsand the 6200 series microprocessors, all available from IntelCorporation. Microprocessor 202 is connected to other elements in device10 through a series of electrical connections to its various input andoutput pins. Microprocessor 202 has an IRQ input line which allows it toreceive signals from various devices. Appropriate interrupt firmware isprovided which receives and reacts to the signals detected on the IRQline.

In addition to the microprocessor 202, other internal devices of thedevice 10 are shown schematically in FIG. 2. These include: display 14;speaker 16; keypad 24; communication sub-system 206; short-rangecommunication sub-system 208; auxiliary I/O devices 210; serial port212; microphone port 214 for microphone 28; flash memory 216 (whichprovides persistent storage of data); random access memory (RAM) 218;clock 220 and other device sub-systems (not shown). Device 10 ispreferably a two-way radio frequency (RF) communication device havingvoice and data communication capabilities. In addition, device 10preferably has the capability to communicate with other computer systemsvia the Internet.

Operating system software executed by the microprocessor 202 ispreferably stored in a computer-readable medium, such as flash memory216, but may be stored in other types of memory devices, such asread-only memory (ROM) or similar storage element. In addition, systemsoftware, specific device applications, or parts thereof, may betemporarily loaded into a volatile store, such as RAM 218. Communicationsignals received by the mobile device may also be stored to RAM 218.

Microprocessor 202, in addition to its operating system functions,enables execution of software applications on device 10. A set ofsoftware (or firmware) applications, generally identified asapplications 222, that control basic device operations, such as voicecommunication module 222A and data communication module 222B, may beinstalled on the device 10 during manufacture or downloaded thereafter.As well, additional software modules, such as software module 222N,which may be for instance a personal information manager (PIM)application, may be installed during manufacture or downloadedthereafter into device 10. Data associated with each application can bestored in flash memory 216.

Communication functions, including data and voice communications, areperformed through the communication sub-system 206 and the short-rangecommunication sub-system 208. Collectively, sub-systems 206 and 208provide the signal-level interface for all communication technologiesprocessed by device 10. Various applications 222 provide the operationalcontrols to further process and log the communications. Communicationsub-system 206 includes receiver 224, transmitter 226 and one or moreantennas, illustrated as receive antenna 228 and transmit antenna 230.In addition, communication sub-system 206 also includes processingmodules, such as digital signal processor (DSP) 232 and localoscillators (LOs) 234. The specific design and implementation ofcommunication sub-system 206 is dependent upon the communication networkin which device 10 is intended to operate. For example, communicationsub-system 206 of device 10 may operate with the Mobitex (trade-mark),DataTAC (trade-mark) or General Packet Radio Service (GPRS) mobile datacommunication networks and also operate with any of a variety of voicecommunication networks, such as Advanced Mobile Phone Service (AMPS),Time Division Multiple Access (TDMA), Code Division Multiple Access(CDMA), CDMA 2000, Personal Communication Service (PCS), Global Systemfor Mobile Communication (GSM), etc. Other types of data and voice(telephonic) networks, both separate and integrated, may also beutilized with device 10. In any event, communication sub-system 206provides device 10 with the capability of communicating with otherdevices using various communication technologies, including instantmessaging (IM) systems, text messaging (TM) systems and short messageservice (SMS) systems.

In addition to processing communication signals, DSP 232 providescontrol of receiver 224 and transmitter 226. For example, gains appliedto communication signals in receiver 224 and transmitter 226 may beadaptively controlled through automatic gain-control algorithmsimplemented in DSP 232.

In a data communication mode, a received signal, such as a text messageor Web page download, is processed by the communication sub-system 206and is provided as an input to microprocessor 202. The received signalis then further processed by microprocessor 202 which can then generatean output to display 14 or to an auxiliary I/O device 210. A device usermay also compose data items, such as e-mail messages, using keypad 24,trackball 20 and/or some other auxiliary I/O device 210, such as atouchpad, a rocker switch, a trackball or some other input device. Thecomposed data items may then be transmitted over communication network140 via communication sub-system 206. Sub-system 206 may also detectwhen it is out of communication range for its remote systems.

In a voice communication mode, overall operation of device 10 issubstantially similar to the data communication mode, except thatreceived signals are output to speaker 16, and signals for transmissionare generated by microphone 28. Alternative voice or audio I/Osub-systems, such as a voice message recording sub-system, may also beimplemented on device 10. In addition, display 14 may also be utilizedin voice communication mode, for example, to display the identity of acalling party, the duration of a voice call, or other voice call-relatedinformation.

Short-range communication sub-system 208 enables communication betweendevice 10 and other proximate systems or devices, which need notnecessarily be similar devices. For example, the short-rangecommunication sub-system may include an infrared device and associatedcircuits and components, or a Bluetooth (trade-mark) communicationmodule to provide for communication with similarly enabled systems anddevices. Although not shown, sub-system 208 may be connected totransmitter 226 to provide physical transmissions of its signals.

Powering the entire electronics of the mobile handheld communicationdevice is power source 236. In one embodiment, the power source 236includes one or more batteries. In another embodiment, the power source236 is a single battery pack, especially a rechargeable battery pack. Apower switch (not shown) provides an “on/off” switch for device 10. Apower source interface (not shown) may be provided in hardware,firmware, software or a combination of such elements to selectivelycontrol access of components in device 10 to power source 236. Powerfrom source 236 may be provided to one or more components in device 10,including components in transmitter 226. Voltages from battery 236 maybe provided to voltage regulators (not shown) in device 10, forsubsequent use by components in device 10. Upon activation of the powerswitch an application 222 is initiated to turn on device 10. Upondeactivation of the power switch, an application 222 is initiated toturn off device 10. Power to device 10 may also be controlled by otherdevices and by software applications 222.

Further detail is now provided on aspects of an embodiment relating to asystem and method for controlling an RF transmission from device 10.Referring to FIG. 3, further detail on transmitter 226 is shown.Therein, transmitter 226 comprises power amplifier 300 which sends andreceives signals to and from RF transceiver 310. Signals provided fromDSP 232 to transmitter 226 through transceiver 310 include signals thatare ultimately destined to be converted into an analog radio signal thatis modulated and transmitted as a wireless signal through antenna 230.Signals provided from transmitter 226 to DSP 232 include operationalsignals relating to the modulation of the signals provided by DSP 232.In transmitter 226, signals from DSP 232 are provided to power amplifier300. An exemplary power amplifier is 6037R2 Freescale (trademark). Asnoted in the background section, one factor in the amount of unwantedradio frequency noise is the electrical matching of transmitter 226 topower amplifier 300. Power amplifier 300, as shown, may produce lessadditional noise if transmitter 226 appears as about a 50 ohm load tothe output of amplifier 300.

The following components are provided in the output path of an outputsignal generated by amplifier 300 that is destined for transmissionthrough antenna 230. First, the raw output from power amplifier 300 isprovided as an analog signal having a voltage signals to filter module302, which provide some initial filtering of the raw signal. Afterfilter module 302, the (filtered) signal is provided to delay element304, which functionally provides a time delay of the output signalwithout attenuating its output levels. After the output signal isdelayed, it is provided to harmonic filter 306. Harmonic filter 306further shapes the output signal to filter signals outside of apredetermined frequency range. In one embodiment, delaying the outputsignal delay element 304 before having harmonic filter 306 further shapethe signal provides additional attenuation of harmonics in the outputsignal.

The output of harmonic filter 306 is provided to antenna matching module308, which provides some frequency matching circuits for the outputsignal. The output signal from module 308 is provided to antenna 230which converts the analog signal into a wireless radio signal that isbroadcasted from device 10.

It will be appreciated that in other embodiments, different arrangementof the modules shown in FIG. 3 may be provided. As an example, filterelements 302 and delay element 304 may be switched in order of locationfrom the output of power amplifier 300. As a further example, elementsin harmonic filter 306 and delay element 304 may be switched in order oflocation from the output of power amplifier 300. Further additionalmodules may be provided or selected modules may be removed fromtransmitter 226. A notable feature of any arrangement is that the delayelement is preferably located in the chain of components prior toelements that provide the substantial filtering of harmonics, such asthe circuits provided in harmonic filter 306.

Referring to FIG. 4, further detail is provided on the element shown inthe block diagram of transmitter 226 in FIG. 3, shown generally at 400.As a physical implementation for transmitter 226, its components andcircuits typically are provided on a printed circuit board (PCB). As isknown in the art, a PCB provides a substrate for mounting and securingcomponents of a circuit thereto. Electrical connections betweencomponents in the circuit can be provided by conductive tracks embeddedin the PCB that run between the related terminals of the connectedcomponents. Specific locations are provided for components of thecircuit and the locations are frequently shown in an outline with anycircuit reference identifiers in a silk screen on the PCB. On the PCB,conductive pads on the surface of the PCB are provided to align with theterminals for the components of the circuit. The pads provide thecontact point for the terminals to the tracks. When assembling thecomponents of the circuit onto the PCB, an automated “pick and place”insertion machine in the manufacturing line can be loaded with therelevant components for the circuit and can be programmed to insert thecomponents at their predetermined location on the PCB. Some componentsin the circuit may be surface mount packages; others may be through-holecomponents; still other components may require manual insertion into theproper location on the PCB. As components are provided in a series ofstandardized package sizes, it is possible to place a differentcomponent in the location for an intended component in the circuit.

Filter module 302 of FIG. 3 is shown in FIG. 4 and provides power andimpedance matching of the output circuit attached to the output of poweramplifier 300. The tuning of the impedance and power characteristics ofan input point of the circuit may not match with the exactcharacteristics of the output of the amplifier. One part of the filtermodule is a notch filter. The filter comprises capacitor 402, resistor404, inductor 408, and capacitor 410, providing a notch filter to reducethe harmonics around 5 GHz. Capacitor 402 is another component in module302 and is placed in series with the output of amplifier 300 for RFcoupling and DC blocking. Resistor 404 is another component in module302 acts as a shunt to ground for the RF stability of the poweramplifier. As parts of module 302 are implemented preferably to providepower and impedance signal matching for amplifier 300, components ofmodule 302 are preferably placed as close as possible to the output ofamplifier 300.

The output of notch filter 406 is provided to delay element 304. Incircuit 400, delay element 304 is presented as a circuit template and asa second low pass filter 412, comprising resistor 414 placed in seriesto the output from notch filter 406 with capacitors 416 and 418 placedas shunts to ground on each terminal of resistor 414. The output ofdelay element 304 is provided to inductor 420 which acts as anelectrostatic protection component for errant discharges received fromantenna 430 to prevent such discharges from reaching power amplifier300. As such, it is preferable that inductor 420 be placed as close aspossible to antenna 430.

For the embodiment, delay element 304 is implemented by replacingcomponents for low pass filter 412 with selected, electrically neutralcomponents. In particular, delay element 304 is implemented bypopulating the location for resistor 414 in the PCB of device 10 with an0 ohm component and not populating components in locations forcapacitors 416 and 418. As such, the delay provided by delay element 304is the propagation time taken for the output signal to traverse throughthe track on the PCB of device 10 connecting the output of filter 406through the 0 ohm component to inductor 420. In one embodiment thephysical package for the 0 ohm resistor is a “0402” sized component. Itwill be appreciated that any 0 ohm-rated component may be used in thelocation for device 414, including 0 ohm components and in certainimplementations, and specially implemented tracks in the PCB of device10, as described below. In other embodiments, delay element 304 may bemoved to be located between inductor 426 and switch connector 422. Inother embodiments, delay element 304 (or its equivalents) may be placedanywhere between the output of amplifier 300 and the input to filter 424(or its equivalent).

In other embodiments, the amount of time of the delay may be shortenedby effectively reducing the length of the track in the connectionbetween power amp 300 and filter 304 in the PCB. In other embodiments,the delay amount may be lengthened by effectively increasing the lengthof the track in the connection between power amp 300 and filter 304 inthe PCB. Lengthening the length of the track may be effectivelyaccomplished by having a series of 0 ohm resistors located in the track.Also, different 0 ohm resistors may have different signal timingpropagation characteristics that may be used as part of the timing forthe delay in element 304. In some embodiments, it may be possible toinsert an inductor in place of a 0 ohm resistor or in addition to a 0ohm resistor. Use of an inductor generally changes the phase of theoutput signal. As such, use of an inductor may be appropriate fordistinct circuit and timing parameters for the delay element 304.

In other embodiments, the delay may be provided by a functioning lowpass filter populated into the components of low pass filter 412. Thefunctioning low-pass filter may be designed to provide a portion of alow-pass filter required by the parameters of the output for poweramplifier 300. Use of such a functioning low pass filter will effect thephase of the output signal. In other embodiments, it may be possible touse a high pass, band pass or notch filter with specific operationalparameters to populate the components in filter 412.

Further still, in other embodiments, additional tracks or circuits maybe provided on the PCB and may be selectively bridged into the signalpath of delay element 304. For example, a separate parallel track may beprovided in the PCB, with a first gapped connection point at or near thephysical junction of the common terminal for resistor 414 and capacitor418 and a second gapped connection point at or near the physicaljunction of the common terminal for resistor 414 and capacitor 416. Thegaps of the connection points may be bridged by the population of a 0ohm resistor at each point. The separate parallel track may also haveadditional circuitry or pads for such circuitry provided therein.Alternatively, one end of the parallel track may be connected at onejunction point and another end of the parallel track may have the gappedconnection point to another junction point. Alternatively oradditionally, a specific track may be laid in PCB as part of aconnection point between any components in the circuit of transmitter226 that imparts a known signal propagation delay for a voltagetraversing the length of the track, thereby imparting a comparable delayas provided by the delay element, or its equivalents as described above.The track may be placed at any appropriate location, as described abovefor the delay element between components prior to the harmonic filter.

From delay element 304, the next stage for the output harmonic filter306 consists of switch connector 422 and harmonic filter 306. Switchconnector 422 may provide an additional delay to the output signal as ittraverses through it on its way to harmonic filter 306. The switchconnector is used as a device to selectively “open” the switch from itsnormally closed state, allowing measurement of RF signals of the outputof the device during testing, manufacturing or repair. Harmonic filter306 is a low pass filter 424 consisting of inductor 426 and capacitors428. Capacitors 428 are located on each terminal of inductor 426 andthey each provide a shunt to ground. The output of the low pass filter424 is the output of filter 306 and is provided to antenna connector430. In the embodiment, the low pass filter provides a pass band from DCto 2 GHz. It is used to attenuate harmonics above 3.4 GHz, representingthe second and third harmonics of signals in the DCS band (1747 MHz) andPCS band (1880 MHz).

It would be appreciated that the specific values of the elements in FIG.4 can be selected to tune for various frequencies to allow signals indifferent frequencies to pass or to attenuate signals in selectedfrequency ranges.

In other embodiments, different PCB tracks may be provided for thecomponents in the output circuit for transmitter 226. As such, delayelement 304 may be replaced with a dedicated, calibrated delay componentand pads for capacitors 416 and 418 may be eliminated.

FIG. 5A shows a Smith plot of an exemplary output real and imaginarycomponents of a prior art RF transmission circuit. FIG. 5B shows a Smithplot of real and imaginary output components from the circuit of FIG. 4.In comparison with FIG. 5A, the chart in FIG. 5B shows that the locationof mark 5 at 2.472 GHz, which is the third harmonic of 824 MHz, issignificantly changed due to the delay element.

Referring to FIG. 6, schematic 600 shows additional filtering componentsaround power amplifier 300. As noted in the background section above, anunwanted source of radio frequency transmissions is leakagetransmissions that are emitted from power amplifier 300 to its supplybattery through the connecting tracks on the PCB. The filters assist inreducing these unwanted noise transmissions, thereby reducing the amountof noise and additional harmonics imposed on the output signal of poweramplifier 300 through the battery, such as battery 236. For theoperating parameters of an embodiment, the filtering may be set toattenuate signals above 2 GHz.

Power amplifier 300 generates output signals using RF signal provided bythe transceiver. The supply voltage for amplifier 300 originates frombattery 236. Two power supplies are provided, namely VBat signal 602 andVReg signal 604. VBat is a high current, 3.8 volt DC supply. VReg is lowcurrent voltage input to internal voltage regulator (not shown) indevice 10 and is a 2.7 volt DC supply.

VBat signal 602 is provided to power amplifier 300 through ferrite beads606 to the Final and Driver voltage input terminals for the low band(LB) and high band (HB) power input pin for amplifier 300. Beads 606 areinductors providing high energy chokes, absorbing high frequency signalsemanating from amplifier 300 to VBat. Any equivalent high frequencychoke may be used. Ferrite beads 606 are placed in series in each powertrack between VBat 604 and power amplifier 300. Bead 606A is locatedbetween the HB power signal and VBat. In the PCB track connecting thebattery to the LB power lines, a set of beads 606B and 606C may beplaced in parallel in the circuit to increase the amount of filteringprovided.

Also, capacitors sets 608A and 608B are located between the outputs ofbeads 606 and the input pin of amplifier 300. Capacitors 608A are 0.01μF and 1000 pF. Capacitors 608B are 33 pF and 0.01 μF. Capacitors 608Aand 608B filter feedback harmonics leaking from amplifier 300 thatradiate along the tracks of PCB that ultimately connect VBat signal 602to amplifier 300.

Capacitors 610 have a nominal value of 10 pF and are located on theinput side of beads 606 between the input terminals of beads 606 andVBat 602 signal. Capacitors 610 also act to filter radio frequencyharmonics from amplifier 300.

Capacitor 612 has a nominal value of 100 μF and is located nearcapacitors 610 on the same track. Its relatively large value is selectedto filter out second harmonics from amplifier 300.

It will be appreciated that other filter circuits and other values forcapacitors shown in FIGS. 4 and 6 may be provided in other embodiments.The target frequencies for the filters can be changed depending on thetarget fundamental transmission frequency and its harmonics. However,for the circuits as shown, their filters are designed to operate aroundthe 2 GHz bandwidth range as device 10 as described, provides quad-bandcommunications, which may generate second, third, fourth and otherharmonics generated around any transmissions for the 800, 900, 1800,and/or 1900 MHz frequency bands. It will be appreciated that otherfiltering systems may be provided for other transmission bands and/orother harmonics.

In other embodiments, a method of attenuating harmonics of an outputsignal may be provided by implementing filtering and delay stepscomparable to filtering and delay components described in the circuitsherein.

The present invention is defined by the claims appended hereto, with theforegoing description being merely illustrative of embodiments of theinvention. Those of ordinary skill may envisage certain modifications tothe foregoing embodiments which, although not explicitly discussedherein, do not depart from the scope of the invention, as defined by theappended claims.

1. An electronic circuit for reducing harmonics of an output signal froma power amplifier in a radio frequency transmission circuit for awireless communication device, comprising: a printed circuit board(PCB); a power amplifier for generating an output signal for saidcommunication device; and a circuit implemented on the PCB connected toan output terminal of said power amplifier for said output signal, saidcircuit comprising a first filtering stage; a delay element and aharmonic filter, wherein in said circuit, said delay element is locatedbetween said harmonic filter and said output terminal and said delayelement provides a timing delay in the output signal; and said harmonicfilter is a low pass filter having a frequency cut-off point thatattenuates first order harmonics of said output signal.
 2. Theelectronic circuit for reducing harmonics of an output signal from apower amplifier as claimed in claim 1, wherein said delay element is a 0ohm component.
 3. The electronic circuit for reducing harmonics of anoutput signal from a power amplifier as claimed in claim 2, wherein saiddelay element replaces a component of a filter element in said circuit.4. The electronic circuit for reducing harmonics of an output signalfrom a power amplifier as claimed in claim 3, wherein said harmonicfilter implements the filter element that the delay element replaced. 5.The electronic circuit for reducing harmonics of an output signal from apower amplifier as claimed in claim 2, wherein said filtering stagecomprises a notch filter to attenuate signals about the 5 GHz frequencyband.
 6. The electronic circuit for reducing harmonics of an outputsignal from a power amplifier as claimed in claim 5, wherein saidfiltering stage further comprises a low pass filter to attenuate signalsover the 5 GHz frequency band.
 7. The electronic circuit for reducingharmonics of an output signal from a power amplifier as claimed in claim1, wherein said delay element replaces a filter element in said circuitutilizing an inductor in place of a component of the filter element. 8.The electronic circuit for reducing harmonics of an output signal from apower amplifier as claimed in claim 1, wherein said delay elementcomprises an alternative track in said PCB that is selectively connectedto said circuit by insertion of at least one 0 ohm component to completean electronic connection between said track and said circuit.
 9. Theelectronic circuit for reducing harmonics of an output signal from apower amplifier as claimed in claim 1, further comprising capacitors toreduce transmission of signals from said power amplifier in tracks inthe PCB of a power connection circuit connecting the power amplifier toa battery for said amplifier.
 10. The electronic circuit for reducingharmonics of an output signal from a power amplifier as claimed in claim9, wherein a set of said capacitors are located in said power connectioncircuit between a high filter choke and said power amplifier.
 11. Theelectronic circuit for reducing harmonics of an output signal from apower amplifier as claimed in claim 10, wherein said set of saidcapacitors provide a low pass filter to attenuate signals over the 2 GHzfrequency band.
 12. The electronic circuit for reducing harmonics of anoutput signal from a power amplifier as claimed in claim 10, wherein asecond set of said capacitors are located in said power connectioncircuit between said high filter choke and battery.
 13. The electroniccircuit for reducing harmonics of an output signal from a poweramplifier as claimed in claim 12, wherein said second set of saidcapacitors provide a low pass filter to attenuate signals over the 2 GHzfrequency band.
 14. The electronic circuit for reducing harmonics of anoutput signal from a power amplifier as claimed in claim 9, wherein aninput point on said circuit is tuned to accommodate power and impedancecharacteristics of an output of said power amplifier.
 15. The electroniccircuit for reducing harmonics of an output signal from a poweramplifier as claimed in claim 1, wherein said delay element is a trackin said PCB that has sufficient length providing a propagation delay fora signal to traverse said length to provide said timing delay.
 16. Amethod of reducing harmonics of an output signal from a power amplifierin a radio frequency transmission circuit for a wireless communicationdevice, comprising: providing a first filtering stage for said outputsignal; providing a harmonic filter to said output signal after saidfirst filtering stage; providing an output stage for said output signalafter said harmonic filter; and providing a dedicated delay elementbefore said harmonic filter for said output signal to impart a timedelay for the output signal, causing harmonics of the output signal tobe reduced, wherein said harmonic filter is a low pass filter having afrequency cut-off point that attenuates first order harmonics of saidoutput signal.
 17. The method of reducing harmonics of an output signalfrom a power amplifier as claimed in claim 16, wherein said delayelement is a 0 ohm component.
 18. The method of reducing harmonics of anoutput signal from a power amplifier as claimed in claim 17, whereinsaid delay element replaces a component of a filter element in saidcircuit.
 19. The method of reducing harmonics of an output signal from apower amplifier as claimed in claim 18, further comprising filteringtransmission of signals from said power amplifier in a power connectioncircuit connecting the power amplifier to a battery for said amplifier.